Honors & Awards
Breast Cancer Research Program Breakthrough Award, Department of Defense - Congressionally Directed Medical Research Programs (2015)
Innovative Development and Exploratory Award, California Breast Cancer Research Program (2013)
Research Award, American Society for Mass Spectrometry (2012)
McCormick Faculty Award, Stanford University School of Medicine (2012)
Developmental Cancer Research Award, Stanford Cancer Institute (2011, 2013)
Post Doctoral, Fred Hutchinson Cancer Research Center (2010)
PhD, Purdue University, Chemistry (2005)
BA, Carleton College, Chemistry (2001)
Current Research and Scholarly Interests
The Pitteri laboratory is focused on the discovery and validation of proteins that can be used as molecular indicators of risk, diagnosis, progression, and recurrence of cancer. Proteomic technologies, predominantly mass spectrometry, are used to identify proteins in the blood that are differentially regulated and/or post-translationally modified with disease state. Using human plasma samples, tumor tissue, cancer cell lines, and genetically engineered mouse models, the origins of these proteins are being investigated. A major goal of this research is to define novel molecular signatures for breast and ovarian cancers, including particular sub-types of these diseases. This laboratory is also focused on the identification of proteins with expression restricted to the surface of cancer cells which can be used as novel targets for molecular imaging technologies.
Independent Studies (6)
- Directed Reading in Radiology
RAD 299 (Aut, Win, Spr, Sum)
- Early Clinical Experience in Radiology
RAD 280 (Aut, Win, Spr, Sum)
- Graduate Research
RAD 399 (Aut, Win, Spr, Sum)
- Medical Scholars Research
RAD 370 (Aut, Win, Spr, Sum)
- Readings in Radiology Research
RAD 101 (Aut, Win, Spr, Sum)
- Undergraduate Research
RAD 199 (Aut, Win, Spr, Sum)
- Directed Reading in Radiology
Parallel Comparison of N-Linked Glycopeptide Enrichment Techniques Reveals Extensive Glycoproteomic Analysis of Plasma Enabled by SAX-ERLIC.
Journal of proteome research
2017; 16 (3): 1249-1260
Protein glycosylation is of increasing interest due to its important roles in protein function and aberrant expression with disease. Characterizing protein glycosylation remains analytically challenging due to its low abundance, ion suppression issues, and microheterogeneity at glycosylation sites, especially in complex samples such as human plasma. In this study, the utility of three common N-linked glycopeptide enrichment techniques is compared using human plasma. By analysis on an LTQ-Orbitrap Elite mass spectrometer, electrostatic repulsion hydrophilic interaction liquid chromatography using strong anion exchange solid-phase extraction (SAX-ERLIC) provided the most extensive N-linked glycopeptide enrichment when compared with multilectin affinity chromatography (M-LAC) and Sepharose-HILIC enrichments. SAX-ERLIC enrichment yielded 191 unique glycoforms across 72 glycosylation sites from 48 glycoproteins, which is more than double that detected using other enrichment techniques. The greatest glycoform diversity was observed in SAX-ERLIC enrichment, with no apparent bias toward specific glycan types. SAX-ERLIC enrichments were additionally analyzed by an Orbitrap Fusion Lumos mass spectrometer to maximize glycopeptide identifications for a more comprehensive assessment of protein glycosylation. In these experiments, 829 unique glycoforms were identified across 208 glycosylation sites from 95 plasma glycoproteins, a significant improvement from the initial method comparison and one of the most extensive site-specific glycosylation analysis in immunodepleted human plasma to date. Data are available via ProteomeXchange with identifier PXD005655.
View details for DOI 10.1021/acs.jproteome.6b00849
View details for PubMedID 28199111
Development of IsoTaG, a Chemical Glycoproteomics Technique for Profiling Intact N- and O-Glycopeptides from Whole Cell Proteomes.
Journal of proteome research
Protein glycosylation can have an enormous variety of biological consequences, reflecting the molecular diversity encoded in glycan structures. This same structural diversity has imposed major challenges on the development of methods to study the intact glycoproteome. We recently introduced a method termed isotope-targeted glycoproteomics (IsoTaG), which utilizes isotope recoding to characterize azidosugar-labeled glycopeptides bearing fully intact glycans. Here, we describe the broad application of the method to analyze glycoproteomes from a collection of tissue-diverse cell lines. The effort was enabled by a new high-fidelity pattern-searching and glycopeptide validation algorithm termed IsoStamp v2.0, as well as by novel stable isotope probes. Application of the IsoTaG platform to 15 cell lines metabolically labeled with Ac4GalNAz or Ac4ManNAz revealed 1375 N- and 2159 O-glycopeptides, variously modified with 74 discrete glycan structures. Glycopeptide-bound glycans observed by IsoTaG were found to be comparable to released N-glycans identified by permethylation analysis. IsoTaG is therefore positioned to enhance structural understanding of the glycoproteome.
View details for DOI 10.1021/acs.jproteome.6b01053
View details for PubMedID 28244757
Multi-Lectin Affinity Chromatography for Separation, Identification, and Quantitation of Intact Protein Glycoforms in Complex Biological Mixtures.
Methods in molecular biology (Clifton, N.J.)
2017; 1550: 99-113
Protein glycosylation is considered to be one of the most abundant post-translational modifications and is recognized for playing key roles in cellular functions. Aberrant N-linked glycosylation has been associated with several human diseases and has prompted the development and constant improvement of analytical tools to separate, characterize, and quantify glycoproteins in complex mixtures extracted from various biological samples (such as blood and tissue). Lectins, or carbohydrate-binding proteins, have been used as valuable tools for enriching for glycoproteins and selecting for specific types of glycosylation. Herein a method using multidimensional intact protein fractionation and LC-MS/MS analysis is described. Immunodepletion is used to remove highly abundant proteins from human plasma, followed by glycoform separation using multi-lectin affinity chromatography, in which specific lectins are chosen to capture and elute specific types of glycosylation. Reversed-phase chromatography prior to digestion is used for further fractionation, allowing for an increased number of protein identifications of moderate- to low-abundant proteins detectable in plasma. This method also incorporates isotopic labeling during alkylation for relative quantitation between two samples (such as a case and control). A bottom-up, tandem mass spectrometry-based proteomics approach is used for protein identification and quantitation, and allows for screening glycoform-specific changes across hundreds of plasma proteins.
View details for DOI 10.1007/978-1-4939-6747-6_9
View details for PubMedID 28188526
Activation of Notch1 synergizes with multiple pathways in promoting castration-resistant prostate cancer
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2016; 113 (42): E6457-E6466
Metastatic castration-resistant prostate cancer (CRPC) is the primary cause of prostate cancer-specific mortality. Defining new mechanisms that can predict recurrence and drive lethal CRPC is critical. Here, we demonstrate that localized high-risk prostate cancer and metastatic CRPC, but not benign prostate tissues or low/intermediate-risk prostate cancer, express high levels of nuclear Notch homolog 1, translocation-associated (Notch1) receptor intracellular domain. Chronic activation of Notch1 synergizes with multiple oncogenic pathways altered in early disease to promote the development of prostate adenocarcinoma. These tumors display features of epithelial-to-mesenchymal transition, a cellular state associated with increased tumor aggressiveness. Consistent with its activation in clinical CRPC, tumors driven by Notch1 intracellular domain in combination with multiple pathways altered in prostate cancer are metastatic and resistant to androgen deprivation. Our study provides functional evidence that the Notch1 signaling axis synergizes with alternative pathways in promoting metastatic CRPC and may represent a new therapeutic target for advanced prostate cancer.
View details for DOI 10.1073/pnas.1614529113
View details for Web of Science ID 000385610400019
View details for PubMedID 27694579
Proteomic Analysis of Epithelial to Mesenchymal Transition (EMT) Reveals Cross-talk between SNAIL and HDAC1 Proteins in Breast Cancer Cells.
Molecular & cellular proteomics
2016; 15 (3): 906-917
Epithelial to mesenchymal transition (EMT)(1) occurs naturally during embryogenesis, tissue repair, cancer progression, and metastasis. EMT induces cellular and microenvironmental changes resulting in loss of epithelial and acquisition of mesenchymal phenotypes, which promotes cellular invasive and migratory capabilities. EMT can be triggered by extracellular factors, including TGF-β, HGF, and EGF. Overexpression of transcription factors, such as SNAIL, SLUG, ZEB1/2, and TWIST1, also induces EMT and is correlated to cancer aggressiveness. Here, the breast adenocarcinoma cell line MCF7 was transduced with SNAIL to identify specific mechanisms controlled by this transcription factor during EMT. Overexpression of SNAIL led to EMT, which was thoroughly validated by molecular, morphological, and functional experiments. Subcellular proteome enrichment followed by GEL-LC-MS/MS was performed to provide extensive protein fractionation and in-depth proteomic analysis. Quantitative analysis relied on a SILAC strategy, using the invasive breast cancer cell line MDA-MB-231 as a reference for quantitation. Subsets of proteins enriched in each subcellular compartment led to a complementary list of 4289 proteins identified with high confidence. A subset of differentially expressed proteins was validated by Western blot, including regulation in specific cellular compartments, potentially caused by protein translocation. Protein network analysis highlighted complexes involved in cell cycle control and epigenetic regulation. Flow cytometry analysis indicated that SNAIL overexpression led to cell cycle arrest in G0/G1 phases. Furthermore, down-regulation of HDAC1 was observed, supporting the involvement of epigenetic processes in SNAIL-induced EMT. When HDAC1 activity was inhibited, MCF7 not only apparently initiated EMT but also up-regulated SNAIL, indicating the cross-talk between these two proteins. Both HDAC1 inhibition and SNAIL overexpression activated the AKT pathway. These molecular mechanisms appear to be essential to EMT and therefore for cancer metastasis. Specific control of such epigenetic processes might then represent effective approaches for clinical management of metastatic cancer.
View details for DOI 10.1074/mcp.M115.052910
View details for PubMedID 26764010
FIG4 is a hepatitis C virus particle-bound protein implicated in virion morphogenesis and infectivity with cholesteryl ester modulation potential.
journal of general virology
2016; 97 (1): 69-81
There is growing evidence that virus particles also contain host cell proteins, which provide viruses with certain properties required for entry and release. A proteomic analysis performed on double gradient-purified hepatitis C virus from two highly viremic patients identified the Phosphatidylinositol 3,5-bisphosphate 5-phosphatase FIG4 (KIAA0274) as part of the viral particles. We validated the association using immunoelectron microscopy, immunoprecipitation and neutralization assays in vitro as well as patient-derived virus particles. RNAi-mediated reduction of FIG4 expression decreased cholesteryl ester (CE) levels along with intra- and extracellular viral infectivity without affecting HCV RNA levels. Likewise, overexpressing FIG4 increased intracellular CE levels as well as intra- and extracellular viral infectivity without affecting viral RNA levels. Triglyceride (TG) levels and lipid droplets (LD) parameters remained unaffected. The 3,5-bisphosphate 5-phosphatase active site of FIG4 was found to strongly condition these results. While FIG4 was found to localize to areas corresponding to viral assembly sites, at the immediate vicinity of LDs in calnexin+ and HCV core+ regions, no implication of FIG4 in the secretory pathway of the hepatocytes could be found using either FIG4 null mice, in vitro morphometry or functional assays of the ERGIC/Golgi compartments. This indicates that FIG4-dependent modulation of HCV infectivity is unrelated to alterations in the functionality of the secretory pathway. Because of the documented implication of CE in the composition and infectivity of HCV particles, these results suggest that FIG4 binds to HCV and modulates particle formation in a CE-related manner.
View details for DOI 10.1099/jgv.0.000331
View details for PubMedID 26519381
Engineering cancer microenvironments for in vitro 3-D tumor models.
Materials today (Kidlington, England)
2015; 18 (10): 539–53
The natural microenvironment of tumors is composed of extracellular matrix (ECM), blood vasculature, and supporting stromal cells. The physical characteristics of ECM as well as the cellular components play a vital role in controlling cancer cell proliferation, apoptosis, metabolism, and differentiation. To mimic the tumor microenvironment outside the human body for drug testing, two-dimensional (2-D) and murine tumor models are routinely used. Although these conventional approaches are employed in preclinical studies, they still present challenges. For example, murine tumor models are expensive and difficult to adopt for routine drug screening. On the other hand, 2-D in vitro models are simple to perform, but they do not recapitulate natural tumor microenvironment, because they do not capture important three-dimensional (3-D) cell-cell, cell-matrix signaling pathways, and multi-cellular heterogeneous components of the tumor microenvironment such as stromal and immune cells. The three-dimensional (3-D) in vitro tumor models aim to closely mimic cancer microenvironments and have emerged as an alternative to routinely used methods for drug screening. Herein, we review recent advances in 3-D tumor model generation and highlight directions for future applications in drug testing.
View details for DOI 10.1016/j.mattod.2015.05.002
View details for PubMedID 28458612
Intact MicroRNA Analysis Using High Resolution Mass Spectrometry
JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY
2014; 25 (1): 80-87
MicroRNAs (miRNAs) are small single-stranded non-coding RNAs that post-transcriptionally regulate gene expression, and play key roles in the regulation of a variety of cellular processes and in disease. New tools to analyze miRNAs will add understanding of the physiological origins and biological functions of this class of molecules. In this study, we investigate the utility of high resolution mass spectrometry for the analysis of miRNAs through proof-of-concept experiments. We demonstrate the ability of mass spectrometry to resolve and separate miRNAs and corresponding 3' variants in mixtures. The mass accuracy of the monoisotopic deprotonated peaks from various miRNAs is in the low ppm range. We compare fragmentation of miRNA by collision-induced dissociation (CID) and by higher-energy collisional dissociation (HCD) which yields similar sequence coverage from both methods but additional fragmentation by HCD versus CID. We measure the linear dynamic range, limit of detection, and limit of quantitation of miRNA loaded onto a C18 column. Lastly, we explore the use of data-dependent acquisition of MS/MS spectra of miRNA during online LC-MS and demonstrate that multiple charge states can be fragmented, yielding nearly full sequence coverage of miRNA on a chromatographic time scale. We conclude that high resolution mass spectrometry allows the separation and measurement of miRNAs in mixtures and a standard LC-MS setup can be adapted for online analysis of these molecules.
View details for DOI 10.1007/s13361-013-0759-x
View details for Web of Science ID 000329239600010
View details for PubMedID 24174127
Performance evaluation of affinity ligands for depletion of abundant plasma proteins.
Journal of chromatography. B, Analytical technologies in the biomedical and life sciences
2013; 939: 10-16
Human plasma is a commonly used diagnostic fluid in clinical chemistry. In-depth plasma proteomic analysis is performed to search for disease biomarkers, however the large dynamic range of protein abundance in plasma presents a substantial analytical challenge. Removal of abundant plasma proteins using antibody capture approaches is a common and attractive means to reduce sample complexity and to aid the analysis of lower abundance proteins of interest. A novel class of heavy chain camelid-derived affinity ligands produced in Saccharomyces cerevisiae, has recently been developed as an alternative to antibody-based depletion methods. Here, we evaluate the performance characteristics of these ligands for removal of high abundance plasma proteins. Affinity ligands were tested for the removal of 14 abundant human plasma proteins. The performance characteristics were evaluated by gel-electrophoresis and LC-MS/MS of the bound and flow-through fractions. The capacity of a 5.6mL column was found to be 125μL of plasma. Replicate analysis demonstrated high column reproducibility and linearity, efficient removal of abundant proteins, and enrichment of lower abundance proteins observed after depletion. The novel class of affinity ligands provides an attractive alternative to traditional antibody-based immunodepletion methods.
View details for DOI 10.1016/j.jchromb.2013.09.008
View details for PubMedID 24090752
Autoantibody Signatures Involving Glycolysis and Splicesome Proteins Precede a Diagnosis of Breast Cancer among Postmenopausal Women
2013; 73 (5): 1502-1513
We assessed the autoantibody repertoire of a mouse model engineered to develop breast cancer and the repertoire of autoantibodies in human plasmas collected at a preclinical time point and at the time of clinical diagnosis of breast cancer. In seeking to identify common pathways, networks, and protein families associated with the humoral response, we elucidated the dynamic nature of tumor antigens and autoantibody interactions. Lysate proteins from an immortalized cell line from a MMTV-neu mouse model and from MCF7 human breast cancers were spotted onto nitrocellulose microarrays and hybridized with mouse and human plasma samples, respectively. Immunoglobulin-based plasma immunoreactivity against glycolysis and spliceosome proteins was a predominant feature observed both in tumor-bearing mice and in prediagnostic human samples. Interestingly, autoantibody reactivity was more pronounced further away than closer to diagnosis. We provide evidence for dynamic changes in autoantibody reactivity with tumor development and progression that may depend, in part, on the extent of antigen-antibody interactions.
View details for DOI 10.1158/0008-5472.CAN-12-2560
View details for Web of Science ID 000315741500007
View details for PubMedID 23269276
Evaluation of Known Oncoantibodies, HER2, p53, and Cyclin B1, in Prediagnostic Breast Cancer Sera
CANCER PREVENTION RESEARCH
2012; 5 (8): 1036-1043
Serum autoantibodies, directed against oncogenic proteins, have been frequently detected in the sera of patients with breast cancer. It is unknown whether serum antibodies that are identified in patients with established disease could also be detected in patients with newly diagnosed disease or even predate the diagnosis of breast cancer. Using sera collected at the time of treatment, at the time of diagnosis, or before the time of diagnosis, the current study aimed to address the temporal relationship between breast cancer development and serum antibody response. Starting from serum antibodies to eight known breast cancer antigens, we first identified four serum antibodies, HER2/neu, p53, carcinoembryonic antigen (CEA), and cyclin B1, which are significantly increased in the sera collected from patients with breast cancer at the time of treatment. These antibodies were also elevated in breast cancer sera collected at the time of diagnosis. Finally, comparison of antibody responses in prediagnostic samples from women before the development of breast cancer and in controls showed that antibodies to the HER2/neu and p53 can be detected in sera that were collected on average more than 150 days before a breast cancer diagnosis. These results showed that serum autoantibodies commonly reported in sera from patients with established disease can also be detected in prediagnostic sera and may be useful for the early detection of breast cancer.
View details for DOI 10.1158/1940-6207.CAPR-11-0558
View details for Web of Science ID 000308223500006
View details for PubMedID 22715141
Quantitative Proteomic Profiling Identifies Protein Correlates to EGFR Kinase Inhibition
MOLECULAR CANCER THERAPEUTICS
2012; 11 (5): 1071-1081
Clinical oncology is hampered by lack of tools to accurately assess a patient's response to pathway-targeted therapies. Serum and tumor cell surface proteins whose abundance, or change in abundance in response to therapy, differentiates patients responding to a therapy from patients not responding to a therapy could be usefully incorporated into tools for monitoring response. Here, we posit and then verify that proteomic discovery in in vitro tissue culture models can identify proteins with concordant in vivo behavior and further, can be a valuable approach for identifying tumor-derived serum proteins. In this study, we use stable isotope labeling of amino acids in culture (SILAC) with proteomic technologies to quantitatively analyze the gefitinib-related protein changes in a model system for sensitivity to EGF receptor (EGFR)-targeted tyrosine kinase inhibitors. We identified 3,707 intracellular proteins, 1,276 cell surface proteins, and 879 shed proteins. More than 75% of the proteins identified had quantitative information, and a subset consisting of 400 proteins showed a statistically significant change in abundance following gefitinib treatment. We validated the change in expression profile in vitro and screened our panel of response markers in an in vivo isogenic resistant model and showed that these were markers of gefitinib response and not simply markers of phospho-EGFR downregulation. In doing so, we also were able to identify which proteins might be useful as markers for monitoring response and which proteins might be useful as markers for a priori prediction of response.
View details for DOI 10.1158/1535-7163.MCT-11-0852
View details for Web of Science ID 000307984800003
View details for PubMedID 22411897
Microparticles From Ovarian Carcinomas Are Shed Into Ascites and Promote Cell Migration
INTERNATIONAL JOURNAL OF GYNECOLOGICAL CANCER
2012; 22 (4): 546-552
Microparticles are cellular-derived vesicles (0.5-1.0 μm) composed of cell membrane components, which are actively shed from the surface of various cells, including epithelial cells. We compared microparticles in ascites between women with ovarian carcinoma and women with benign ovarian pathology, and isolated tumor-derived (epithelial cell adhesion molecule [EpCAM]-positive) microparticles for functional analysis and proteomics.Cases included 8 patients with benign ovarian neoplasms and 41 with ovarian carcinoma. Ascites from a high-grade stage III serous carcinoma was used for functional and proteomic analysis. Cancer cells were isolated using EpCAM-coated beads, microparticles were isolated by ultracentrifugation/flow cytometry, and sorting was achieved using markers (eg, EpCAM). Binding and migrations assays were performed with 3 ovarian cancer cell lines. Proteomic analysis of EpCAM-positive microparticles and ascites cancer cells was performed by mass spectrometry.Microparticles in benign pelvic fluid were similar to early and advanced-stage ascites (2.4 vs 2.8 vs 2.0 × 10⁶ microparticles/mL). Advanced stage had a greater proportion of EpCAM-positive microparticles than early or benign disease (13.3% vs 2.5% vs 2.1%; P = 0.001), and serous histology had more than endometrioid (13.2% vs 1.8%; P = 0.01). Microparticles bound to the surface of 3 cultured cell lines, and were internalized into the EpCAM-positive microparticles, resulting in more cell migration than buffer alone or EpCAM-negative microparticles (P = 0.007). A dose-dependent increase was seen with increasing numbers of EpCAM-positive microparticles. Proteomics revealed that most proteins in EPCAM-positive microparticles were shared with cancer cells, and many are associated with cell motility and invasion, such as fibronectin, filamin A, vimentin, myosin-9, and fibrinogen.Ascites from advanced-stage and serous ovarian carcinomas contain large numbers of tumor-derived microparticles. In vitro, these microparticles bind to cancer cells and stimulate migration. Tumor-derived microparticles in ascites could mediate the predilection for peritoneal spread in serous ovarian carcinomas.
View details for DOI 10.1097/IGC.0b013e318241d9b9
View details for Web of Science ID 000303546100005
View details for PubMedID 22315094
Concordant Release of Glycolysis Proteins into the Plasma Preceding a Diagnosis of ER+ Breast Cancer
2012; 72 (8): 1935-1942
Although the identification of peripheral blood biomarkers would enhance early detection strategies for breast cancer, the discovery of protein markers has been challenging. In this study, we sought to identify coordinated changes in plasma proteins associated with breast cancer based on large-scale quantitative mass spectrometry. We analyzed plasma samples collected up to 74 weeks before diagnosis from 420 estrogen receptor (ER)(+) cases and matched controls enrolled in the Women's Health Initiative cohort. A gene set enrichment analysis was applied to 467 quantified proteins, linking their corresponding genes to particular biologic pathways. On the basis of differences in the concentration of individual proteins, glycolysis pathway proteins exhibited a statistically significant difference between cases and controls. In particular, the enrichment was observed among cases in which blood was drawn closer to diagnosis (effect size for the 0-38 weeks prediagnostic group, 1.91; P, 8.3E-05). Analysis of plasmas collected at the time of diagnosis from an independent set of cases and controls confirmed upregulated levels of glycolysis proteins among cases relative to controls. Together, our findings indicate that the concomitant release of glycolysis proteins into the plasma is a pathophysiologic event that precedes a diagnosis of ER(+) breast cancer.
View details for DOI 10.1158/0008-5472.CAN-11-3266
View details for Web of Science ID 000302905700005
View details for PubMedID 22367215
Increased Plasma Levels of the APC-Interacting Protein MAPRE1, LRG1, and IGFBP2 Preceding a Diagnosis of Colorectal Cancer in Women
CANCER PREVENTION RESEARCH
2012; 5 (4): 655-664
Longitudinal blood collections from cohort studies provide the means to search for proteins associated with disease before clinical diagnosis. We investigated plasma samples from the Women's Health Initiative (WHI) cohort to determine quantitative differences in plasma proteins between subjects subsequently diagnosed with colorectal cancer (CRC) and matched controls that remained cancer-free during the period of follow-up. Proteomic analysis of WHI samples collected before diagnosis of CRC resulted in the identification of six proteins with significantly (P < 0.05) elevated concentrations in cases compared with controls. Proteomic analysis of two CRC cell lines showed that five of the six proteins were produced by cancer cells. Microtubule-associated protein RP/EB family member 1 (MAPRE1), insulin-like growth factor-binding protein 2 (IGFBP2), leucine-rich alpha-2-glycoprotein (LRG1), and carcinoembryonic antigen (CEA) were individually assayed by enzyme linked immunosorbent assay (ELISA) in 58 pairs of newly diagnosed CRC samples and controls and yielded significant elevations (P < 0.05) among cases relative to controls. A combination of these four markers resulted in a receiver operating characteristics curve with an area under the curve value of 0.841 and 57% sensitivity at 95% specificity. This combination rule was tested in an independent set of WHI samples collected within 7 months before diagnosis from cases and matched controls resulting in 41% sensitivity at 95% specificity. A panel consisting of CEA, MAPRE1, IGFBP2, and LRG1 has predictive value in prediagnostic CRC plasmas.
View details for DOI 10.1158/1940-6207.CAPR-11-0412
View details for Web of Science ID 000302572400020
View details for PubMedID 22277732
Lung Cancer Signatures in Plasma Based on Proteome Profiling of Mouse Tumor Models
2011; 20 (3): 289-299
We investigated the potential of in-depth quantitative proteomics to reveal plasma protein signatures that reflect lung tumor biology. We compared plasma protein profiles of four mouse models of lung cancer with profiles of models of pancreatic, ovarian, colon, prostate, and breast cancer and two models of inflammation. A protein signature for Titf1/Nkx2-1, a known lineage-survival oncogene in lung cancer, was found in plasmas of mouse models of lung adenocarcinoma. An EGFR signature was found in plasma of an EGFR mutant model, and a distinct plasma signature related to neuroendocrine development was uncovered in the small-cell lung cancer model. We demonstrate relevance to human lung cancer of the protein signatures identified on the basis of mouse models.
View details for DOI 10.1016/j.ccr.2011.08.007
View details for Web of Science ID 000295205700006
View details for PubMedID 21907921
Tumor Microenvironment-Derived Proteins Dominate the Plasma Proteome Response during Breast Cancer Induction and Progression
2011; 71 (15): 5090-5100
Tumor development relies upon essential contributions from the tumor microenvironment and host immune alterations. These contributions may inform the plasma proteome in a manner that could be exploited for cancer diagnosis and prognosis. In this study, we employed a systems biology approach to characterize the plasma proteome response in the inducible HER2/neu mouse model of breast cancer during tumor induction, progression, and regression. Mass spectrometry data derived from approximately 1.6 million spectra identified protein networks involved in wound healing, microenvironment, and metabolism that coordinately changed during tumor development. The observed alterations developed prior to cancer detection, increased progressively with tumor growth and reverted toward baseline with tumor regression. Gene expression and immunohistochemical analyses suggested that the cancer-associated plasma proteome was derived from transcriptional responses in the noncancerous host tissues as well as the developing tumor. The proteomic signature was distinct from a nonspecific response to inflammation. Overall, the developing tumor simultaneously engaged a number of innate physiologic processes, including wound repair, immune response, coagulation and complement cascades, tissue remodeling, and metabolic homeostasis that were all detectable in plasma. Our findings offer an integrated view of tumor development relevant to plasma-based strategies to detect and diagnose cancer.
View details for DOI 10.1158/0008-5472.CAN-11-0568
View details for Web of Science ID 000293267600006
View details for PubMedID 21653680
A Proteomics Platform Combining Depletion, Multi-lectin Affinity Chromatography (M-LAC), and Isoelectric Focusing to Study the Breast Cancer Proteome
2011; 83 (12): 4845-4854
The discovery of breast cancer associated plasma/serum biomarkers is important for early diagnosis, disease mechanism elucidation, and determination of treatment strategy for the disease. In this study of serum samples, a multidimensional fractionation platform combined with mass spectrometric analysis were used to achieve the identification of medium to lower abundance proteins, as well as to simultaneously detect glycan and abundance changes. Immuno-affinity depletion and multi-lectin chromatography (M-LAC) were integrated into an automated HPLC platform to remove high abundance protein and fractionate glycoproteins. The collected glycoproteomes were then subjected to isoelectric focusing (IEF) separation by a digital ProteomeChip (dPC), followed by in-gel digestion and LC-MS analysis using an Orbitrap mass spectrometer. As a result, the total number of identified proteins increased significantly when the IEF fractionation step was included as part of the platform. Relevant proteins with biological and disease significance were observed and the dynamic range of the serum proteome measurement was extended. In addition, potential glycan changes were indicated by comparing proteins in control and cancer samples in terms of their affinity to the multi-lectin column (M-LAC) and the pI profiles in IEF separation. In conclusion, a proteomics platform including high abundance protein depletion, lectin affinity fractionation, IEF separation, and LC-MS analysis has been applied to discover breast cancer-associated proteins. The following candidates, thrombospondin-1 and 5, alpha-1B-glycoprotein, serum amyloid P-component, and tenascin-X, were selected as promising examples of the use of this platform. They show potential abundance and glycan changes and will be further investigated in future studies.
View details for DOI 10.1021/ac2002802
View details for Web of Science ID 000291499800035
View details for PubMedID 21513341
Plasma Proteome Profiles Associated with Inflammation, Angiogenesis, and Cancer
2011; 6 (5)
Tumor development is accompanied by a complex host systemic response, which includes inflammatory and angiogenic reactions. Both tumor-derived and systemic response proteins are detected in plasma from cancer patients. However, given their non-specific nature, systemic response proteins can confound the detection or diagnosis of neoplasia. Here, we have applied an in-depth quantitative proteomic approach to analyze plasma protein changes in mouse models of subacute irritant-driven inflammation, autoreactive inflammation, and matrix associated angiogenesis and compared results to previously described findings from mouse models of polyoma middle T-driven breast cancer and Pdx1-Cre Kras(G12D) Ink4a/Arf (lox/lox)-induced pancreatic cancer. Among the confounding models, approximately 1/3 of all quantified plasma proteins exhibited a significant change in abundance compared to control mice. Of the proteins that changed in abundance, the majority were unique to each model. Altered proteins included those involved in acute phase response, inflammation, extracellular matrix remodeling, angiogenesis, and TGFβ signaling. Comparison of changes in plasma proteins between the confounder models and the two cancer models revealed proteins that were restricted to the cancer-bearing mice, reflecting the known biology of these tumors. This approach provides a basis for distinguishing between protein changes in plasma that are cancer-related and those that are part of a non-specific host response.
View details for DOI 10.1371/journal.pone.0019721
View details for Web of Science ID 000290531100023
View details for PubMedID 21589862
Confounding Effects of Hormone Replacement Therapy in Protein Biomarker Studies
CANCER EPIDEMIOLOGY BIOMARKERS & PREVENTION
2011; 20 (1): 134-139
We have recently investigated effects of hormone replacement therapy (HRT) on the serum proteome, and found a high proportion of proteins with altered levels associated with oral estrogen and/or estrogen plus progesterone treatment. Given this finding, we have investigated the extent to which exposure to HRT may have a confounding effect in the assessment of circulating proteins as cancer biomarkers.We utilize mass spectrometry data collected from the HRT serum proteome studies to estimate the overall effect of postmenopausal hormone therapy on candidate ovarian cancer biomarkers that have been previously reported.Levels of approximately half of the proteins reported as potential ovarian cancer biomarkers were found to be affected by HRT. The impact of HRT on levels of insulin-like growth factor and inhibin protein families was found to be substantial.We conclude that the potential confounding effect of HRT and other types of exposures should be taken into consideration in cancer biomarker study design.HRT significantly affects the serum proteome and should be taken into account as part of biomarker study design and data analysis.
View details for DOI 10.1158/1055-9965.EPI-10-0673
View details for Web of Science ID 000285972800014
View details for PubMedID 21037107
Detection of Elevated Plasma Levels of Epidermal Growth Factor Receptor Before Breast Cancer Diagnosis among Hormone Therapy Users
2010; 70 (21): 8598-8606
Applying advanced proteomic technologies to prospectively collected specimens from large studies is one means of identifying preclinical changes in plasma proteins that are potentially relevant to the early detection of diseases such as breast cancer. We conducted 14 independent quantitative proteomics experiments comparing pooled plasma samples collected from 420 estrogen receptor-positive (ER(+)) breast cancer patients ≤17 months before their diagnosis and matched controls. Based on the more than 3.4 million tandem mass spectra collected in the discovery set, 503 proteins were quantified, of which 57 differentiated cases from controls with a P value of <0.1. Seven of these proteins, for which quantitative ELISA assays were available, were assessed in an independent validation set. Of these candidates, epidermal growth factor receptor (EGFR) was validated as a predictor of breast cancer risk in an independent set of preclinical plasma samples for women overall [odds ratio (OR), 1.44; P = 0.0008] and particularly for current users of estrogen plus progestin (E + P) menopausal hormone therapy (OR, 2.49; P = 0.0001). Among current E + P users, the EGFR sensitivity for breast cancer risk was 31% with 90% specificity. Whereas the sensitivity and specificity of EGFR are insufficient for a clinically useful early detection biomarker, this study suggests that proteins that are elevated preclinically in women who go on to develop breast cancer can be discovered and validated using current proteomic technologies. Further studies are warranted to examine the role of EGFR and to discover and validate other proteins that could potentially be used for early detection of breast cancer.
View details for DOI 10.1158/0008-5472.CAN-10-1676
View details for Web of Science ID 000283667300038
View details for PubMedID 20959476
The development of an integrated platform to identify breast cancer glycoproteome changes in human serum
34th International Symposium on High Performance Liquid Phase Separations and Related Techniques
ELSEVIER SCIENCE BV. 2010: 3307–15
Protein glycosylation represents one of the major post-translational modifications and can have significant effects on protein function. Moreover, changes in the carbohydrate structure are increasingly being recognized as an important modification associated with cancer etiology. In this report, we describe the development of a proteomics approach to identify breast cancer related changes in either concentration and/or the carbohydrate structures of glycoprotein(s) present in blood samples. Diseased and healthy serum samples were processed by an optimized sample preparation protocol using multiple lectin affinity chromatography (M-LAC) that partitions serum proteins based on glycan characteristics. Subsequently, three separate procedures, 1D SDS-PAGE, isoelectric focusing and an antibody microarray, were applied to identify potential candidate markers for future study. The combination of these three platforms is illustrated in this report with the analysis of control and cancer glycoproteomic fractions. Firstly, a molecular weight based separation of glycoproteins by 1D SDS-PAGE was performed, followed by protein, glycoprotein staining, lectin blotting and LC-MS analysis. To refine or confirm the list of interesting glycoproteins, isoelectric focusing (targeting sialic acid changes) and an antibody microarray (used to detect neutral glycan shifts) were selected as the orthogonal methods. As a result, several glycoproteins including alpha-1B-glycoprotein, complement C3, alpha-1-antitrypsin and transferrin were identified as potential candidates for further study.
View details for DOI 10.1016/j.chroma.2009.09.029
View details for Web of Science ID 000277757100018
View details for PubMedID 19782370
Elafin Is a Biomarker of Graft-Versus-Host Disease of the Skin
SCIENCE TRANSLATIONAL MEDICINE
2010; 2 (13)
Graft-versus-host disease (GVHD), the major complication of allogeneic bone marrow transplantation, affects the skin, liver, and gastrointestinal tract. There are no plasma biomarkers specific for any acute GVHD target organ. We used a large-scale quantitative proteomic discovery procedure to identify biomarker candidates of skin GVHD and validated the lead candidate, elafin, with enzyme-linked immunosorbent assay in samples from 492 patients. Elafin was overexpressed in GVHD skin biopsies. Plasma concentrations of elafin were significantly higher at the onset of skin GVHD, correlated with the eventual maximum grade of GVHD, and were associated with a greater risk of death relative to other known risk factors (hazard ratio, 1.78). We conclude that elafin has significant diagnostic and prognostic value as a biomarker of skin GVHD.
View details for DOI 10.1126/scitranslmed.3000406
View details for Web of Science ID 000277263500004
View details for PubMedID 20371463
Novel proteins associated with risk for coronary heart disease or stroke among postmenopausal women identified by in-depth plasma proteome profiling.
2010; 2 (7): 48-?
Coronary heart disease (CHD) and stroke were key outcomes in the Women's Health Initiative (WHI) randomized trials of postmenopausal estrogen and estrogen plus progestin therapy. We recently reported a large number of changes in blood protein concentrations in the first year following randomization in these trials using an in-depth quantitative proteomics approach. However, even though many affected proteins are in pathways relevant to the observed clinical effects, the relationships of these proteins to CHD and stroke risk among postmenopausal women remains substantially unknown.The same in-depth proteomics platform was applied to plasma samples, obtained at enrollment in the WHI Observational Study, from 800 women who developed CHD and 800 women who developed stroke during cohort follow-up, and from 1-1 matched controls. A plasma pooling strategy, followed by extensive fractionation prior to mass spectrometry, was used to identify proteins related to disease incidence, and the overlap of these proteins with those affected by hormone therapy was examined. Replication studies, using enzyme-linked-immunosorbent assay (ELISA), were carried out in the WHI hormone therapy trial cohorts.Case versus control concentration differences were suggested for 37 proteins (nominal P < 0.05) for CHD, with three proteins, beta-2 microglobulin (B2M), alpha-1-acid glycoprotein 1 (ORM1), and insulin-like growth factor binding protein acid labile subunit (IGFALS) having a false discovery rate < 0.05. Corresponding numbers for stroke were 47 proteins with nominal P < 0.05, three of which, apolipoprotein A-II precursor (APOA2), peptidyl-prolyl isomerase A (PPIA), and insulin-like growth factor binding protein 4 (IGFBP4), have a false discovery rate < 0.05. Other proteins involved in insulin-like growth factor signaling were also highly ranked. The associations of B2M with CHD (P < 0.001) and IGFBP4 with stroke (P = 0.005) were confirmed using ELISA in replication studies, and changes in these proteins following the initiation of hormone therapy use were shown to have potential to help explain hormone therapy effects on those diseases.In-depth proteomic discovery analysis of prediagnostic plasma samples identified B2M and IGFBP4 as risk markers for CHD and stroke respectively, and provided a number of candidate markers of disease risk and candidate mediators of hormone therapy effects on CHD and stroke.ClinicalTrials.gov identifier: NCT00000611.
View details for DOI 10.1186/gm169
View details for PubMedID 20667078
A systems approach to the proteomic identification of novel cancer biomarkers
2010; 28 (4): 233-239
The proteomics field has experienced rapid growth with technologies achieving ever increasing accuracy, sensitivity, and throughput, and with availability of computational tools to address particular applications. Given that the proteome represents the most functional component encoded for in the genome, a systems approach to disease investigations and biomarker identification benefits substantially from integration of proteome level studies. Here we present proteomic approaches that have allowed systematic searches for potential cancer markers by integrating cancer cell profiling with additional sources of data, as illustrated with recent studies of ovarian cancer.
View details for DOI 10.3233/DMA-2010-0696
View details for Web of Science ID 000279321200005
View details for PubMedID 20534908
Integrated Proteomic Analysis of Human Cancer Cells and Plasma from Tumor Bearing Mice for Ovarian Cancer Biomarker Discovery
2009; 4 (11)
The complexity of the human plasma proteome represents a substantial challenge for biomarker discovery. Proteomic analysis of genetically engineered mouse models of cancer and isolated cancer cells and cell lines provide alternative methods for identification of potential cancer markers that would be detectable in human blood using sensitive assays. The goal of this work is to evaluate the utility of an integrative strategy using these two approaches for biomarker discovery.We investigated a strategy that combined quantitative plasma proteomics of an ovarian cancer mouse model with analysis of proteins secreted or shed by human ovarian cancer cells. Of 106 plasma proteins identified with increased levels in tumor bearing mice, 58 were also secreted or shed from ovarian cancer cells. The remainder consisted primarily of host-response proteins. Of 25 proteins identified in the study that were assayed, 8 mostly secreted proteins common to mouse plasma and human cancer cells were significantly upregulated in a set of plasmas from ovarian cancer patients. Five of the eight proteins were confirmed to be upregulated in a second independent set of ovarian cancer plasmas, including in early stage disease.Integrated proteomic analysis of cancer mouse models and human cancer cell populations provides an effective approach to identify potential circulating protein biomarkers.
View details for DOI 10.1371/journal.pone.0007916
View details for Web of Science ID 000272004600018
View details for PubMedID 19936259
Application of serum proteomics to the Women's Health Initiative conjugated equine estrogens trial reveals a multitude of effects relevant to clinical findings.
2009; 1 (4): 47-?
The availability of serum collections from the Women's Health Initiative (WHI) conjugated equine estrogens (CEE) randomized controlled trial provides an opportunity to test the potential of in-depth quantitative proteomics to uncover changes in the serum proteome related to CEE and to assess their relevance to trial findings, including elevations in the risk of stroke and venous thromboembolism and a reduction in fractures.Five independent large scale quantitative proteomics analyses were performed, each comparing a set of pooled serum samples collected from 10 subjects, 1 year following initiation of CEE at 0.625 mg/d, relative to their baseline pool. A subset of proteins that exhibited increased levels with CEE by quantitative proteomics was selected for validation studies.Of 611 proteins quantified based on differential stable isotope labeling, the levels of 116 (19%) were changed after 1 year of CEE (nominal P < 0.05), while 64 of these had estimated false discovery rates <0.05. Most of the changed proteins were not previously known to be affected by CEE and had relevance to processes that included coagulation, metabolism, osteogenesis, inflammation, and blood pressure maintenance. To validate quantitative proteomic data, 14 proteins were selected for ELISA. Findings for ten - IGF1, IGFBP4, IGFBP1, IGFBP2, F10, AHSG, GC, CP, MMP2, and PROZ - were confirmed in the initial set of 50 subjects and further validated in an independent set of 50 additional subjects who received CEE.CEE affected a substantial fraction of the serum proteome, including proteins with relevance to findings from the WHI CEE trial related to cardiovascular disease and fracture.ClinicalTrials.gov identifier: NCT00000611.
View details for DOI 10.1186/gm47
View details for PubMedID 19402886
Postmenopausal estrogen and progestin effects on the serum proteome.
2009; 1 (12): 121-?
Women's Health Initiative randomized trials of postmenopausal hormone therapy reported intervention effects on several clinical outcomes, with some important differences between estrogen alone and estrogen plus progestin. The biologic mechanisms underlying these effects, and these differences, have yet to be fully elucidated.Baseline serum samples were compared with samples drawn 1 year later for 50 women assigned to active hormone therapy in both the estrogen-plus-progestin and estrogen-alone randomized trials, by applying an in-depth proteomic discovery platform to serum pools from 10 women per pool.In total, 378 proteins were quantified in two or more of the 10 pooled serum comparisons, by using strict identification criteria. Of these, 169 (44.7%) showed evidence (nominal P < 0.05) of change in concentration between baseline and 1 year for one or both of estrogen-plus-progestin and estrogen-alone groups. Quantitative changes were highly correlated between the two hormone-therapy preparations. A total of 98 proteins had false discovery rates < 0.05 for change with estrogen plus progestin, compared with 94 for estrogen alone. Of these, 84 had false discovery rates <0.05 for both preparations. The observed changes included multiple proteins relevant to coagulation, inflammation, immune response, metabolism, cell adhesion, growth factors, and osteogenesis. Evidence of differential changes also was noted between the hormone preparations, with the strongest evidence in growth factor and inflammation pathways.Serum proteomic analyses yielded a large number of proteins similarly affected by estrogen plus progestin and by estrogen alone and identified some proteins and pathways that appear to be differentially affected between the two hormone preparations; this may explain their distinct clinical effects.
View details for DOI 10.1186/gm121
View details for PubMedID 20034393
Occurrence of Autoantibodies to Annexin I, 14-3-3 Theta and LAMR1 in Prediagnostic Lung Cancer Sera
JOURNAL OF CLINICAL ONCOLOGY
2008; 26 (31): 5060-5066
We have implemented a high throughput platform for quantitative analysis of serum autoantibodies, which we have applied to lung cancer for discovery of novel antigens and for validation in prediagnostic sera of autoantibodies to antigens previously defined based on analysis of sera collected at the time of diagnosis.Proteins from human lung adenocarcinoma cell line A549 lysates were subjected to extensive fractionation. The resulting 1,824 fractions were spotted in duplicate on nitrocellulose-coated slides. The microarrays produced were used in a blinded validation study to determine whether annexin I, PGP9.5, and 14-3-3 theta antigens previously found to be targets of autoantibodies in newly diagnosed patients with lung cancer are associated with autoantibodies in sera collected at the presymptomatic stage and to determine whether additional antigens may be identified in prediagnostic sera. Individual sera collected from 85 patients within 1 year before a diagnosis of lung cancer and 85 matched controls from the Carotene and Retinol Efficacy Trial (CARET) cohort were hybridized to individual microarrays.We present evidence for the occurrence in lung cancer sera of autoantibodies to annexin I, 14-3-3 theta, and a novel lung cancer antigen, LAMR1, which precede onset of symptoms and diagnosis.Our findings suggest potential utility of an approach to diagnosis of lung cancer before onset of symptoms that includes screening for autoantibodies to defined antigens.
View details for DOI 10.1200/JCO.2008.16.2388
View details for Web of Science ID 000260537600012
View details for PubMedID 18794547
Precursor-ion mass re-estimation improves peptide identification on hybrid instruments
JOURNAL OF PROTEOME RESEARCH
2008; 7 (9): 4031-4039
Mass spectrometry-based proteomics experiments have become an important tool for studying biological systems. Identifying the proteins in complex mixtures by assigning peptide fragmentation spectra to peptide sequences is an important step in the proteomics process. The 1-2 ppm mass-accuracy of hybrid instruments, like the LTQ-FT, has been cited as a key factor in their ability to identify a larger number of peptides with greater confidence than competing instruments. However, in replicate experiments of an 18-protein mixture, we note parent masses deviate 171 ppm, on average, for ion-trap data directed identifications and 8 ppm, on average, for preview Fourier transform (FT) data directed identifications. These deviations are neither caused by poor calibration nor by excessive ion-loading and are most likely due to errors in parent mass estimation. To improve these deviations, we introduce msPrefix, a program to re-estimate a peptide's parent mass from an associated high-accuracy full-scan survey spectrum. In 18-protein mixture experiments, msPrefix parent mass estimates deviate only 1 ppm, on average, from the identified peptides. In a cell lysate experiment searched with a tolerance of 50 ppm, 2295 peptides were confidently identified using native data and 4560 using msPrefixed data. Likewise, in a plasma experiment searched with a tolerance of 50 ppm, 326 peptides were identified using native data and 1216 using msPrefixed data. msPrefix is also able to determine which MS/MS spectra were possibly derived from multiple precursor ions. In complex mixture experiments, we demonstrate that more than 50% of triggered MS/MS may have had multiple precursor ions and note that spectra with multiple candidate ions are less likely to result in an identification using TANDEM. These results demonstrate integration of msPrefix into traditional shotgun proteomics workflows significantly improves identification results.
View details for DOI 10.1021/pr800307m
View details for Web of Science ID 000259015500038
View details for PubMedID 18707148
Proteomic Analysis of Ovarian Cancer Cells Reveals Dynamic Processes of Protein Secretion and Shedding of Extra-Cellular Domains
2008; 3 (6)
Elucidation of the repertoire of secreted and cell surface proteins of tumor cells is relevant to molecular diagnostics, tumor imaging and targeted therapies. We have characterized the cell surface proteome and the proteins released into the extra-cellular milieu of three ovarian cancer cell lines, CaOV3, OVCAR3 and ES2 and of ovarian tumor cells enriched from ascites fluid.To differentiate proteins released into the media from protein constituents of media utilized for culture, cells were grown in the presence of [(13)C]-labeled lysine. A biotinylation-based approach was used to capture cell surface associated proteins. Our general experimental strategy consisted of fractionation of proteins from individual compartments followed by proteolytic digestion and LC-MS/MS analysis. In total, some 6,400 proteins were identified with high confidence across all specimens and fractions.Protein profiles of the cell lines had substantial similarity to the profiles of human ovarian cancer cells from ascites fluid and included protein markers known to be associated with ovarian cancer. Proteomic analysis indicated extensive shedding from extra-cellular domains of proteins expressed on the cell surface, and remarkably high secretion rates for some proteins (nanograms per million cells per hour). Cell surface and secreted proteins identified by in-depth proteomic profiling of ovarian cancer cells may provide new targets for diagnosis and therapy.
View details for DOI 10.1371/journal.pone.0002425
View details for Web of Science ID 000263280700011
View details for PubMedID 18560578
Isoform analysis of LC-MS/MS data from multidimensional fractionation of the serum proteome
JOURNAL OF PROTEOME RESEARCH
2008; 7 (6): 2546-2552
We developed a visualization approach for the identification of protein isoforms, precursor/mature protein combinations, and fragments from LC-MS/MS analysis of multidimensional fractionation of serum and plasma proteins. We also describe a pattern recognition algorithm to automatically detect and flag potentially heterogeneous species of proteins in proteomic experiments that involve extensive fractionation and result in a large number of identified serum or plasma proteins in an experiment. Examples are given of proteins with known isoforms that validate our approach and present a subset of precursor/mature protein pairs that were detected with this approach. Potential applications include identification of differentially expressed isoforms in disease states.
View details for DOI 10.1021/pr7007219
View details for Web of Science ID 000256599000037
View details for PubMedID 18419151
A mouse to human search for plasma Proteome changes associated with pancreatic tumor development
2008; 5 (6): 953-967
The complexity and heterogeneity of the human plasma proteome have presented significant challenges in the identification of protein changes associated with tumor development. Refined genetically engineered mouse (GEM) models of human cancer have been shown to faithfully recapitulate the molecular, biological, and clinical features of human disease. Here, we sought to exploit the merits of a well-characterized GEM model of pancreatic cancer to determine whether proteomics technologies allow identification of protein changes associated with tumor development and whether such changes are relevant to human pancreatic cancer.Plasma was sampled from mice at early and advanced stages of tumor development and from matched controls. Using a proteomic approach based on extensive protein fractionation, we confidently identified 1,442 proteins that were distributed across seven orders of magnitude of abundance in plasma. Analysis of proteins chosen on the basis of increased levels in plasma from tumor-bearing mice and corroborating protein or RNA expression in tissue documented concordance in the blood from 30 newly diagnosed patients with pancreatic cancer relative to 30 control specimens. A panel of five proteins selected on the basis of their increased level at an early stage of tumor development in the mouse was tested in a blinded study in 26 humans from the CARET (Carotene and Retinol Efficacy Trial) cohort. The panel discriminated pancreatic cancer cases from matched controls in blood specimens obtained between 7 and 13 mo prior to the development of symptoms and clinical diagnosis of pancreatic cancer.Our findings indicate that GEM models of cancer, in combination with in-depth proteomic analysis, provide a useful strategy to identify candidate markers applicable to human cancer with potential utility for early detection.
View details for DOI 10.1371/journal.pmed.0050123
View details for Web of Science ID 000257105600020
View details for PubMedID 18547137
Mining the plasma proteome for cancer biomarkers
2008; 452 (7187): 571-579
Systematic searches for plasma proteins that are biological indicators, or biomarkers, for cancer are underway. The difficulties caused by the complexity of biological-fluid proteomes and tissue proteomes (which contribute proteins to plasma) and by the extensive heterogeneity among diseases, subjects and levels of sample procurement are gradually being overcome. This is being achieved through rigorous experimental design and in-depth quantitative studies. The expected outcome is the development of panels of biomarkers that will allow early detection of cancer and prediction of the probable response to therapy. Achieving these objectives requires high-quality specimens with well-matched controls, reagent resources, and an efficient process to confirm discoveries through independent validation studies.
View details for DOI 10.1038/nature06916
View details for Web of Science ID 000254567200035
View details for PubMedID 18385731
Plasma proteome profiling of a mouse model of breast cancer identifies a set of up-regulated proteins in common with human breast cancer cells
JOURNAL OF PROTEOME RESEARCH
2008; 7 (4): 1481-1489
We have applied an in-depth quantitative proteomic approach, combining isotopic labeling extensive intact protein separation and mass spectrometry, for high confidence identification of protein changes in plasmas from a mouse model of breast cancer. We hypothesized that a wide spectrum of proteins may be up-regulated in plasma with tumor development and that comparisons with proteins expressed in human breast cancer cell lines may identify a subset of up-regulated proteins in common with proteins expressed in breast cancer cell lines that may represent candidate biomarkers for breast cancer. Plasma from PyMT transgenic tumor-bearing mice and matched controls were obtained at two time points during tumor growth. A total of 133 proteins were found to be increased by 1.5-fold or greater at one or both time points. A comparison of this set of proteins with published findings from proteomic analysis of human breast cancer cell lines yielded 49 proteins with increased levels in mouse plasma that were identified in breast cancer cell lines. Pathway analysis comparing the subset of up-regulated proteins known to be expressed in breast cancer cell lines with other up-regulated proteins indicated a cancer related function for the former and a host-response function for the latter. We conclude that integration of proteomic findings from mouse models of breast cancer and from human breast cancer cell lines may help identify a subset of proteins released by breast cancer cells into the circulation and that occur at increased levels in breast cancer.
View details for DOI 10.1021/pr7007994
View details for Web of Science ID 000254711000013
View details for PubMedID 18311905
A mouse plasma peptide atlas as a resource for disease proteomics
2008; 9 (6)
We present an in-depth analysis of mouse plasma leading to the development of a publicly available repository composed of 568 liquid chromatography-tandem mass spectrometry runs. A total of 13,779 distinct peptides have been identified with high confidence. The corresponding approximately 3,000 proteins are estimated to span a 7 logarithmic range of abundance in plasma. A major finding from this study is the identification of novel isoforms and transcript variants not previously predicted from genome analysis.
View details for DOI 10.1186/gb-2008-9-6-r93
View details for Web of Science ID 000257498000012
View details for PubMedID 18522751
- Proteomic approaches for cancer biomarker discovery in plasma EXPERT REVIEW OF PROTEOMICS 2007; 4 (5): 589-590
Contribution of protein fractionation to depth of analysis of the serum and plasma proteomes
JOURNAL OF PROTEOME RESEARCH
2007; 6 (9): 3558-3565
In-depth analysis of the serum and plasma proteomes by mass spectrometry is challenged by the vast dynamic range of protein abundance and substantial complexity. There is merit in reducing complexity through fractionation to facilitate mass spectrometry analysis of low-abundance proteins. However, fractionation reduces throughput and has the potential of diluting individual proteins or inducing their loss. Here, we have investigated the contribution of extensive fractionation of intact proteins to depth of analysis. Pooled serum depleted of abundant proteins was fractionated by an orthogonal two-dimensional system consisting of anion-exchange and reversed-phase chromatography. The resulting protein fractions were aliquotted; one aliquot was analyzed by shotgun LC-MS/MS, and another was further resolved into protein bands in a third dimension using SDS-PAGE. Individual gel bands were excised and subjected to in situ digestion and mass spectrometry. We demonstrate that increased fractionation results in increased depth of analysis based on total number of proteins identified in serum and based on representation in individual fractions of specific proteins identified in gel bands following a third-dimension SDS gel analysis. An intact protein analysis system (IPAS) based on a two-dimensional plasma fractionation schema was implemented that resulted in identification of 1662 proteins with high confidence with representation of protein isoforms that differed in their chromatographic mobility. Further increase in depth of analysis was accomplished by repeat analysis of aliquots from the same set of two-dimensional fractions resulting in overall identification of 2254 proteins. We conclude that substantial depth of analysis of proteins from milliliter quantities of serum or plasma and detection of isoforms are achieved with depletion of abundant proteins followed by two-dimensional protein fractionation and MS analysis of individual fractions.
View details for DOI 10.1021/pr070233q
View details for Web of Science ID 000249371000023
View details for PubMedID 17696519
Ion/molecule reactions of cation radicals formed from protonated polypeptides via gas-phase ion/ion electron transfer
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2006; 128 (36): 11792-11798
Cation radicals formed via gas-phase electron transfer to multiply protonated polypeptides have been found to react with molecular oxygen. Such cation radicals are of interest within the context of electron transfer dissociation, a phenomenon with high utility for the characterization of peptide and protein primary structures. Most of the cation radicals show the attachment of O(2) under room temperature storage conditions in an electrodynamic ion trap. At higher temperatures and under conditions of collisional activation, the oxygen adduct species lose O(2), HO(*), or HO(2)(*), depending upon the identity of the side chain at the radical site. The fragments containing the C-terminus, the so-called z-ions, which are predominantly radical species, engage in reactions with molecular oxygen. This allows for the facile distinction between z-ions and their complementary even-electron c-ion counterparts. Such a capability has utility in protein identification and characterization via mass spectrometry. Intact electron transfer products also show oxygen attachment. Subsequent activation of such adducts show dissociation behavior very similar to that noted for z-ion adducts. These observations indicate that ion/radical reactions can be used to probe the locations of radical sites in the undissociated electron transfer products as well as distinguish between c- and z-type ions.
View details for DOI 10.1021/ja063248i
View details for Web of Science ID 000240291900027
View details for PubMedID 16953618
Parallel ion parking of protein mixtures
2006; 78 (1): 310-316
The multiple charging phenomenon resulting from electrospray ionization of proteins, while useful for the ability to make several mass measurements on a single component, can lead to highly complex spectra when mixtures are analyzed, as each component can generate multiple ions of distinct mass-to-charge ratio. Ion/ion proton-transfer reactions can overcome this problem by reduction of all components to the +1 charge state, but this typically requires the ability to extend the mass range of the instrument well beyond that available in most commercial instruments. Furthermore, reduction of protein charge to +1 also results in a reduction in detector response. Here it is shown that application of a relatively high amplitude, low-frequency auxiliary ac signal to the end cap electrodes of a 3-D ion trap during an ion/ion reaction can slow the ion/ion reaction rates of ions over a broad m/z range, in a process termed HALF parallel ion parking. Adjustment of the frequency and amplitude of the applied voltage allows the mass range into which the initial ion signal is moved to be controlled, allowing for the simplification of multicomponent mixtures within a mass range that is more commonly available on commercial systems. In addition to decreasing spectral complexity, this is advantageous for mixtures with low-abundance components, as there is less compromise with detector response than in reduction to the +1 charge state. Preliminary evidence also suggests that the ion collision cross section may play an important role in determining which charge states are most significantly inhibited from further ion/ion reactions under a given set of ion parking conditions.
View details for DOI 10.1021/ac0515778
View details for Web of Science ID 000234312300047
View details for PubMedID 16383342
Differentiation of aspartic and isoaspartic acids using electron transfer dissociation
JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY
2006; 17 (1): 15-19
Electron-transfer dissociation allows differentiation of isoaspartic acid and aspartic acid residues using the same c + 57 and z - 57 peaks that were previously observed with electron capture dissociation. These peaks clearly define both the presence and the position of isoaspartic acid residues and they are relatively abundant. The lower resolution of the ion trap instrument makes detection of the aspartic acid residue's diagnostic peak difficult because of interference with side-chain fragment ions from arginine residues, but the aspartic acid residues are still clearly observed in the backbone cleavages and can be inferred from the absence of the isoaspartic acid diagnostic ions.
View details for DOI 10.1016/j.jasms.2005.08.019
View details for Web of Science ID 000234520000003
View details for PubMedID 16338146
- Charge-State Dependent Dissociation of a Trypsin/Inhibitor Complex via Ion Trap Collisional Activation Int J Mass Spectrom 2006; 253 (3): 147-55
Recent developments in the ion/ion chemistry of high-mass multiply charged ions
MASS SPECTROMETRY REVIEWS
2005; 24 (6): 931-958
The ability to form multiply charged high-mass ions in the gas-phase, most notably via electrospray ionization (ESI), has allowed the study of many different combinations of positively and negatively charged ions. The charged products are directly amenable to study with mass spectrometry. Ion/ion reactions have proved to be "universal" in the sense that the high exothermicities and large rate constants associated with essentially any combination of oppositely charged ions lead to reaction regardless of the chemical functionalities associated with the ions. These characteristics make ion/ion reactions potentially analytically useful provided reagent ion densities and spatial overlap of the oppositely charged ions are high. These conditions can be readily met by several instrumental configurations. The focus of this review is to highlight developments in this field since 1998. Novel instrumentation has been developed to study ion/ion reactions, such as atmospheric pressure ion/ion reactors followed by mass analysis, or electrodynamic ion trap mass spectrometers, which are used as reaction vessels at sub-atmospheric pressures. A wide variety of reaction phenomenologies have been observed in various ion/ion reactions, with proton transfer being the most common. New phenomenologies have been observed in the reactions of multiply charged positive ions with singly charged negative ions, including cation transfer and cation exchange. A new series of reactions between multiply charged positive ions and multiply charged negative ions have been made possible by recent instrumentation developments. These reactions have led to the observation of proton transfer and complex formation. These observations have provided new insights into ion/ion reaction dynamics and a bound orbit model appears to best account for experimental results. New applications are also discussed for a several ion/ion reaction.
View details for DOI 10.1002/mas.20048
View details for Web of Science ID 000232751800010
View details for PubMedID 15706594
Electron transfer versus proton transfer in gas-phase ion/ion reactions of polyprotonated peptides
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2005; 127 (36): 12627-12639
The ion/ion reactions of several dozen reagent anions with triply protonated cations of the model peptide KGAILKGAILR have been examined to evaluate predictions of a Landau-Zener-based model for the likelihood for electron transfer. Evidence for electron transfer was provided by the appearance of fragment ions unique to electron transfer or electron capture dissociation. Proton transfer and electron transfer are competitive processes for any combination of anionic and cationic reactants. For reagent anions in reactions with protonated peptides, proton transfer is usually significantly more exothermic than electron transfer. If charge transfer occurs at relatively long distances, electron transfer should, therefore, be favored on kinetic grounds because the reactant and product channels cross at greater distances, provided conditions are favorable for electron transfer at the crossing point. The results are consistent with a model based on Landau-Zener theory that indicates both thermodynamic and geometric criteria apply for electron transfer involving polyatomic anions. Both the model and the data suggest that electron affinities associated with the anionic reagents greater than about 60-70 kcal/mol minimize the likelihood that electron transfer will be observed. Provided the electron affinity is not too high, the Franck-Condon factors associated with the anion and its corresponding neutral must not be too low. When one or the other of these criteria is not met, proton transfer tends to occur essentially exclusively. Experiments involving ion/ion attachment products also suggest that a significant barrier exists to the isomerization between chemical complexes that, if formed, lead to either proton transfer or electron transfer.
View details for DOI 10.1021/ja0526057
View details for Web of Science ID 000232039100053
View details for PubMedID 16144411
Electron-transfer ion/ion reactions of doubly protonated peptides: Effect of elevated bath gas temperature
2005; 77 (17): 5662-5669
In this study, the electron-transfer dissociation (ETD) behavior of cations derived from 27 different peptides (22 of which are tryptic peptides) has been studied in a 3D quadrupole ion trap mass spectrometer. Ion/ion reactions between peptide cations and nitrobenzene anions have been examined at both room temperature and in an elevated temperature bath gas environment to form ETD product ions. From the peptides studied, the ETD sequence coverage tends to be inversely related to peptide size. At room temperature, very high sequence coverage (approximately 100%) was observed for small peptides (< or =7 amino acids). For medium-sized peptides composed of 8-11 amino acids, the average sequence coverage was 46%. Larger peptides with 14 or more amino acids yielded an average sequence coverage of 23%. Elevated-temperature ETD provided increased sequence coverage over room-temperature experiments for the peptides of greater than 7 residues, giving an average of 67% for medium-sized peptides and 63% for larger peptides. Percent ETD, a measure of the extent of electron transfer, has also been calculated for the peptides and also shows an inverse relation with peptide size. Bath gas temperature does not have a consistent effect on percent ETD, however. For the tryptic peptides, fragmentation is localized at the ends of the peptides suggesting that the distribution of charge within the peptide may play an important role in determining fragmentation sites. A triply protonated peptide has also been studied and shows behavior similar to the doubly charged peptides. These preliminary results suggest that for a given charge state there is a maximum size for which high sequence coverage is obtained and that increasing the bath gas temperature can increase this maximum.
View details for DOI 10.1021/ac050666h
View details for Web of Science ID 000231652300043
View details for PubMedID 16131079
SO2- electron transfer ion/ion reactions with disulfide linked polypeptide ions
JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY
2005; 16 (7): 1020-1030
Multiply-charged peptide cations comprised of two polypeptide chains (designated A and B) bound via a disulfide linkage have been reacted with SO2-* in an electrodynamic ion trap mass spectrometer. These reactions proceed through both proton transfer (without dissociation) and electron transfer (with and without dissociation). Electron transfer reactions are shown to give rise to cleavage along the peptide backbone, loss of neutral molecules, and cleavage of the cystine bond. Disulfide bond cleavage is the preferred dissociation channel and both Chain A (or B)-S* and Chain A (or B)-SH fragment ions are observed, similar to those observed with electron capture dissociation (ECD) of disulfide-bound peptides. Electron transfer without dissociation produces [M + 2H]+* ions, which appear to be less kinetically stable than the proton transfer [M + H]+ product. When subjected to collision-induced dissociation (CID), the [M + 2H]+* ions fragment to give products that were also observed as dissociation products during the electron transfer reaction. However, not all dissociation channels noted in the electron transfer reaction were observed in the CID of the [M + 2H]+* ions. The charge state of the peptide has a significant effect on both the extent of electron transfer dissociation observed and the variety of dissociation products, with higher charge states giving more of each.
View details for DOI 10.1016/j.jasms.2005.02.010
View details for Web of Science ID 000230045500006
View details for PubMedID 15914021
Parallel ion parking: Improving conversion of parents to first-generation products in electron transfer dissociation
2005; 77 (10): 3411-3414
Electron-transfer dissociation (ETD) in a tandem mass spectrometer is an analytically useful ion/ion reaction technique for deriving polypeptide sequence information, but its utility can be limited by sequential reactions of the products. Sequential reactions lead to neutralization of some products, as well as to signals from products derived from multiple cleavages that can be difficult to interpret. A method of inhibiting sequential ETD fragmentation in a quadrupole ion trap is demonstrated here for the reaction of a triply protonated peptide with nitrobenzene anions. A tailored waveform (in this case, a filtered noise field) is applied during the ion/ion reaction time to accelerate simultaneously first-generation product ions and thereby inhibit their further reaction. This results in a approximately 50% gain in the relative yield of first-generation products and allows for the conversion of more than 90% of the original parent ions into first-generation products. Gains are expected to be even larger when higher charge-state cations are used, as the rates of sequential reaction become closer to the initial reaction rate.
View details for DOI 10.1021/ac0503613
View details for Web of Science ID 000229206800050
View details for PubMedID 15889938
Electron transfer ion/ion reactions in a three-dimensional quadrupole ion trap: Reactions of doubly and triply protonated peptides with SO2 center dot-
2005; 77 (6): 1831-1839
Ion-ion reactions between a variety of peptide cations (doubly and triply charged) and SO2 anions have been studied in a 3-D quadrupole ion trap, resulting in proton and electron transfer. Electron transfer dissociation (ETD) gives many c- and z-type fragments, resulting in extensive sequence coverage in the case of triply protonated peptides with SO2*-. For triply charged neurotensin, in which a direct comparison can be made between 3-D and linear ion trap results, abundances of ETD fragments relative to one another appear to be similar. Reactions of doubly protonated peptides with SO2*- give much less structural information from ETD than triply protonated peptides. Collision-induced dissociation (CID) of singly charged ions formed in reactions with SO2*- shows a combination of proton and electron transfer products. CID of the singly charged species gives more structural information than ETD of the doubly protonated peptide, but not as much information as ETD of the triply protonated peptide.
View details for DOI 10.1021/ac0483872
View details for Web of Science ID 000227759500039
View details for PubMedID 15762593
Complementary structural information from a tryptic N-linked glycopeptide via electron transfer ion/ion reactions and collision-induced dissociation
JOURNAL OF PROTEOME RESEARCH
2005; 4 (2): 628-632
Glycosylation is an important post-translational modification. Analysis of glycopeptides is difficult using collision-induced dissociation, as it typically yields only information about the glycan structure, without any peptide sequence information. We demonstrate here how a 3D-quadrupole ion trap, using the complementary techniques of collision induced dissociation (CID) and electron-transfer dissociation (ETD), can be used to elucidate the glycan structure and peptide sequence of the N-glycosylated peptide from a fractionated tryptic digest of the lectin from the coral tree, Erythina cristagalli. CID experiments on the multiply protonated glycopeptide ions yield, almost exclusively, cleavage at glycosidic bonds, with little peptide backbone fragmentation. ETD reactions of the triply charged glycopeptide cations with either sulfur dioxide or nitrobenzene anions yield cleavage of the peptide backbone with no loss of the glycan structure. These results show that a 3D-quadrupole ion trap can be used to provide glycopeptide amino acid sequence information as well as information about the glycan structure.
View details for DOI 10.1021/pr049770q
View details for Web of Science ID 000228421900051
View details for PubMedID 15822944
Effects of single amino acid substitution on the collision-induced dissociation of intact protein ions: Turkey ovomucoid third domain
JOURNAL OF PROTEOME RESEARCH
2004; 3 (5): 1033-1041
Expanded understanding of the factors that direct polypeptide ion fragmentation can lead to improved specificity in the use of tandem mass spectrometry for the identification and characterization of proteins. Like the fragmentation of peptide cations, the dissociation of whole protein cations shows several preferred cleavages, the likelihood for which is parent ion charge dependent. While such cleavages are often observed, they are far from universally observed, despite the presence of the residues known to promote them. Furthermore, cleavages at residues not noted to be common in a variety of proteins can be dominant for a particular protein or protein ion charge state. Motivated by the ability to study a small protein, turkey ovomucoid third domain, for which a variety of single amino acid variants are available, the effects of changing the identity of one amino acid in the protein sequence on its dissociation behavior were examined. In particular, changes in amino acids associated with C-terminal aspartic acid cleavage and N-terminal proline cleavage were emphasized. Consistent with previous studies, the product ion spectra were found to be dependent upon the parent ion charge state. Furthermore, the fraction of possible C-terminal aspartic acid cleavages observed to occur for this protein was significantly larger than the fraction of possible N-terminal proline cleavages. In fact, very little N-terminal proline cleavage was noted for the wild-type protein despite the presence of three proline residues in the protein. The addition/removal of proline and aspartic acids was studied along with changes in selected residues adjacent to proline residues. Evidence for inhibition of proline cleavage by the presence of nearby basic residues was noted, particularly if the basic residue was likely to be protonated.
View details for DOI 10.1021/pr049910w
View details for Web of Science ID 000224693800015
View details for PubMedID 15473693
Affecting proton mobility in activated peptide and whole protein ions via lysine guanidination
JOURNAL OF PROTEOME RESEARCH
2004; 3 (1): 46-54
We have evaluated the effect of lysine guanidination in peptides and proteins on the dissociation of protonated ions in the gas phase. The dissociation of guanidinated model peptide ions compared to their unmodified forms showed behavior consistent with concepts of proton mobility as a major factor in determining favored fragmentation channels. Reduction of proton mobility associated with lysine guanidination was reflected by a relative increase in cleavages occurring C-terminal to aspartic acid residues as well as increases in small molecule losses. To evaluate the effect of guanidination on the dissociation behavior of whole protein ions, bovine ubiquitin was selected as a model. Essentially, all of the amide bond cleavages associated with the +10 charge state of fully guanidinated ubiquitin were observed to occur C-terminal to aspartic acid residues, unlike the dissociation behavior of the +10 ion of the unmodified protein, where competing cleavage N-terminal to proline and nonspecific amide bond cleavages were also observed. The +8 and lower charge states of the guanidinated protein showed prominent losses of small neutral molecules. This overall fragmentation behavior is consistent with current hypotheses regarding whole protein dissociation that consider proton mobility and intramolecular charge solvation as important factors in determining favored dissociation channels, and are also consistent with the fragmentation behaviors observed for the guanidinated model peptide ions. Further evaluation of the utility of condensed phase guanidination of whole proteins is necessary but the results described here confirm that guanidination can be an effective strategy for enhancing C-terminal aspartic acid cleavages. Gas phase dissociation exclusively at aspartic acid residues, especially for whole protein ions, could be useful in identifying and characterizing proteins via tandem mass spectrometry of whole protein ions.
View details for DOI 10.1021/pr034054u
View details for Web of Science ID 000189022500004
View details for PubMedID 14998162
Phosphorylation site identification via ion trap tandem mass spectrometry of whole protein and peptide ions: Bovine alpha-crystallin A chain
2003; 75 (23): 6509-6516
Tandem mass spectrometry was applied both to ions of a tryptic fragment and intact protein of bovine alpha-crystallin A chain to localize the single site of phosphorylation. The [M + 19H](19+) to [M + 11H](11+) charge states of both phosphorylated and unphosphorylated bovine alpha-crystallin A chain whole protein ions were subjected to collisional activation in a quadrupole ion trap. Ion parking was used to increase the number of parent ions over that yielded by electrospray. Ion-ion proton-transfer reactions were used to reduce the product ion charge states largely to +1 to simplify spectral interpretation. In agreement with previous studies on whole protein ion fragmentation, both protein forms showed backbone cleavages C-terminal to aspartic acid residues at lower charge states. The phosphorylated protein showed competitive fragmentation between backbone cleavage and the neutral loss of phosphoric acid. Analysis of which backbone cleavage products did or did not contain the phosphate was used to localize the site of phosphorylation to one of two possible serine residues. A tryptic digest of the bovine alpha-crystallin A chain yielded a phosphopeptide containing one missed cleavage site. The peptide provided information complementary to that obtained from the intact protein and localized the modified serine to residue 122. Fragmentation of the triply charged phosphopeptide yielded five possible serine phosphorylation sites. Fragmentation of the doubly charged phosphopeptide, formed by ion/ion proton-transfer reactions, positively identified the phosphorylation site as serine-122.
View details for DOI 10.1021/ac034410s
View details for Web of Science ID 000186986000023
View details for PubMedID 14640721
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